Optical switch with coarse and fine deflectors

ABSTRACT

Optical switching of light is effected between an input and an output utilizing a low-bandwidth actuator and a hi-bandwidth actuator.

PRIORITY INFORMATION

The present application is related to commonly assigned U.S. patentapplication Ser. No. 08/851,379, filed on May 5, 1997 and isincorporated herein by reference.

The present application claims priority from U.S. ProvisionalApplication 60/065,580, filed on Nov. 12, 1997 and is incorporatedherein by reference.

BACKGROUND ART

A number of optical switch technologies are currently used forcontrolling the optical passage of light. With one technology, electriccurrent is applied to a polymer to create a thermal effect that changesa refractive index of a polymer. As the refractive index changes, alight beam passing through the polymer is selectively routed from aninput to an output. Although faster than a comparable mechanical opticalswitch, the switching time of polymer optical switches is limitedsignificantly by the thermal characteristics of the polymer.Additionally, the optical properties of the light transmitted throughthe polymer are undesirably affected by the optical characteristics ofthe polymer.

Another optical switch is disclosed by Leslie A. Field et al., in “The8^(th) International Conference on Solid-State Sensors and Actuators,and Eurosensors IX, Stockholm, Sweden, Jun. 25-29, 1995.” The opticalswitch is micro-machined in silicon and uses a thermally activatedactuator to mechanically move a single send optical fiber relative totwo receive optical fibers. Field et al. exhibits relatively slowmechanical movement due to inherent thermal effects. Additionally, Fieldet al. provides only one degree of optical alignment, resulting ininefficient transfer of light between optical fibers due to slightmisalignments.

Another micro-machined optical switch is disclosed by Levinson in U.S.Pat. No. 4,626,066. Levinson uses a cantilevered micro-machined mirrorthat is electrostatically positioned between a stopped and unstoppedposition. While Levinson's mirror may deflect light between two opticalfibers, as with the aforementioned switch designs, it also is capable ofoptical alignment in only one dimension.

What is needed is an optical switch that provides fast and preciseswitching of light between one input and a plurality of outputs, or viceversa.

SUMMARY OF THE INVENTION

The present invention includes an optical switch for deflecting a beamof light between an input and an output. The optical switch comprises afirst actuator disposed in an optical path of the beam of light betweenthe input and the output and a second actuator disposed in the opticalpath of the beam of light between the input and the output. In anexemplary embodiment, the first actuator comprises a low-bandwidth voicecoil motor. The first actuator further comprises a rotary arm and areflector. The reflector is coupled to the arm such that the beam oflight is deflected by the mirror towards the second actuator. Theoptical switch further comprises a position sensing detector. In thepreferred embodiment, a position of the beam of light is sensed by theposition sensing detector, and the deflection of the beam of light bythe first actuator is a function of the sensed position of the beam oflight. In an exemplary embodiment, the second actuator comprises ahi-bandwidth two-stage voice coil motor and a directing lens, which twodimensionally deflect the beam of light. The optical switch furthercomprises a quad detector array. In the preferred embodiment, a positionof the beam of light is sensed by the quad detector array, and the twodimensional deflection of the beam of light by the second actuator is afunction of the sensed position of the beam of light. In the preferredembodiment, the first and the second actuators individually or incombination selectively deflect the beam of light towards the array oflenses. In the preferred embodiment the second actuator is disposed inthe optical path between the array of lenses and the first actuator. Inone embodiment, the optical switch is used in an optical storage driveto direct the beam of light towards an optical storage location.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are block diagrams of an optical switch of a storage andretrieval system;

FIGS. 3a-3 e, illustrate the optical switch in further detail;

FIGS. 4a-b illustrate an imaging assembly coupled to a set of opticalfibers;

FIG. 5 illustrates the optical switch as used in an exemplary opticalpath;

FIGS. 6a-b illustrate a directing optics in further detail;

FIGS. 7a-e illustrate a first actuator of the present invention infurther detail;

FIG. 8 illustrates an exemplary geometry of a second detector;

FIG. 9 illustrates a servo circuit;

FIG. 10 illustrates outputs of A-D photo-detectors;

FIG. 11 illustrates connections between the A-D photo-detectors and theservo circuit;

FIG. 12, illustrates an exemplary embodiment of pre/post-calibration ofthe optical switch; and

FIGS. 13a-b illustrate two embodiments of a magneto-optical disk drive.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

Referring in detail to the drawings wherein similar parts of theinvention are identified by like reference numerals, there is seen inFIGS. 1 and 2 a block diagram of an optical switch 104. The opticalswitch 104 includes an input port 181 and N output ports 182. In thepreferred embodiment, an outgoing laser beam 191 from a laser source 131is directed along an optical path through the input port 181 towards anactuator assembly 251. A portion of the outgoing laser beam 191, whichis indicated as a first beam 191 a, is routed by the actuator assembly251 towards an imaging assembly 252 and, subsequently, towards one ofthe N output ports 182. FIGS. 1 and 2 illustrate the first beam 191 a asit is directed by the actuator assembly 251 towards different ones ofthe N output ports 182. In an exemplary embodiment N equals 12; however,other values for N are understood to be within the scope of the presentinvention. It is also understood that the while the present invention isdescribed in the context of directing a laser beam between the inputport 181 and the output port 182, the optical switch 104 describedherein could also be used to direct a laser beam between the output port182 and the input port 181.

Referring now to FIGS. 3a-3 e, the optical switch 104 is illustrated infurther detail. In the preferred embodiment, the optical switch 104further includes a first detector 358 and a second detector 359 (FIG.3d), and the actuator assembly 251 includes a first actuator 333 and asecond actuator 334. The first and second actuators 333, 334 are bothdisposed along an optical path between the laser source 131 and a set ofoptical fibers 302. Referring briefly to FIG. 3e, the first actuator 333includes a reflector 373 that is coupled to an actuator arm 371. The arm371 rotates about a pivot axis generally illustrated as P. In thepreferred embodiment, the outgoing laser beam 191 is directed by thereflector 373 (FIG. 3c) towards the second actuator 334. In FIG. 3d, thesecond actuator 334 of the optical switch 104 is illustrated in a sidesectional representation. The second actuator 334 includes a directingoptics 375 and a redirection lens 311. The outgoing laser beam 191passes through the directing optics 375 and is optically separated bythe directing optics 375 into first, second, and third beams 191 a-c,which are respectively directed towards the redirection lens 311, thefirst detector 358, and the second detector 359.

Referring now to FIGS. 4a and 4 b, there is seen an imaging assemblycoupled to a set of optical fibers. The imaging assembly 252 includes anarray of lenses 476 and a set of V-grooves 444. The first beam 191 a isdirected and focused by the redirection lens 311 onto a particular oneof the lenses 476, and the particular lens 476 directs the first beam191 a towards a respective proximal end of one of a set of opticalfibers 302. The proximal ends of each of the optical fibers 302 aredisposed within the set of V grooves 444. The set of V-grooves 444 andthe optical axes of the lenses 476 are aligned such that each of thelenses 476 is focused onto the respective proximal ends of the set ofoptical fibers 302. In an exemplary embodiment, the lenses 476 aremolded plastic lenses that each have a 0.50 mm diameter and are disposedalong a linear axis with a 0.50 mm center to center spacing. In theexemplary embodiment, the optical fibers 302 are 4.0 um diametersingle-mode polarization maintaining optical fibers, and thepolarization axes of the optical fibers 302 are all aligned with respectto each other.

Referring now to FIG. 5, there is seen the optical switch as used in anexemplary optical path. In an exemplary embodiment, a magneto-optical(MO) data storage and retrieval system 500 includes a set ofWinchester-type flying heads 506 that are adapted for use with a set ofdouble-sided first surface MO disks 507 (only one flying head shownflying over one MO disk surface in FIG. 5). The set of flying heads 506are coupled to a rotary actuator magnet and coil assembly (not shown) bya respective suspension 530 and actuator arm 505 so as to be positionedover the surfaces of the set of MO disks 507. In operation, the set ofMO disks 507 are rotated to generate aerodynamic lift forces, whichmaintain the set of flying MO heads 506 in a flying conditionapproximately 15 micro-inches above the upper and lower surfaces of theset of MO disks 507. The lift forces are opposed by equal and oppositespring forces applied by the set of suspensions 530. Duringnon-operation, the set of flying MO heads 506 are maintained staticallyin a storage condition away from the surfaces of the set of MO disks507. System 500 further includes: the laser source 131, the opticalswitch 104, and the set of optical fibers 302. Each of the opticalfibers 302 is preferably coupled through a respective one of the set ofactuator arms 505 and set of suspensions 530 to a respective one of theset of flying MO heads 506.

In an exemplary embodiment, the laser source 131 operates at a singlewavelength, preferably at 635-85 nm within a red region of the visiblelight spectrum; however, it is understood that laser sources operatingat other wavelengths may be used. In the preferred embodiment, the lasersource 131 is a distributed feedback (DFB) diode laser source. A DFBlaser source 131, unlike an RF-modulated Fabry-Perot diode laser,produces a very narrowband single-frequency output due to the use of awavelength selective grating element inside the laser cavity. Linearlypolarized light from a DFB laser source 131 that is launched into aselected one of the polarization maintaining optical fibers 302 exitsthe optical fiber with a polarization state that depends on the relativeorientation between the fiber axes and the incident polarization. Theoutput polarization state is stable in time as long as externalperturbations which alter the fiber birefringence are negligible. Thisbehavior contrasts to that observed when using prior art RF-modulatedFabry-Perot diode laser sources. Fabry-Perot laser diodes arecharacterized by high-frequency fluctuations in their spectral output;therefore, when linearly polarized light is launched into a polarizationmaintaining optical fiber 302, fluctuations in the laser wavelength leadto corresponding polarization fluctuations in the laser light exitingthe output of the optical fiber. The resulting polarization noise islarger than the corresponding DFB diode laser source case owing towavelength dependent mode coupling. Mode coupling in fibers is aphenomenon whereby a small portion of the light that is being guidedalong one polarization axis is coupled into the orthogonal axis byintrinsic or stress-induced defects. In MO recording it is importantthat the polarization noise be kept to a minimum, such that a signal tonoise ration (SNR) in the range of 20-25 dB can be achieved. By using aDFB laser source 131 it is possible to achieve the aforementioned levelof SNR in the magneto-optical (MO) data storage and retrieval system 500when utilizing polarization maintaining optical fiber 302 for thedelivery and return of the signal light to and from the MO disks 507.

The representative optical path of FIG. 5 includes: the laser source131, the optical switch 104, one of the set of optical fibers 302, andone of the set of flying MO heads 506. As described previously, thefirst beam 191 a is directed towards a proximal end of a selected one ofthe optical fibers 302. The linear polarization of the first beam 191 ais preferably aligned in the optical path so as to enter the proximalend of the selected polarization maintaining optical fiber 302 at a 45degree angle relative to the polarization axis of the optical fiber 302.The first beam 191 a is directed by the selected optical fiber 302 toexit a respective distal end of the optical fiber and is furtherdirected by a set of optical elements (as described in commonly assignedU.S. patent application Ser. No. 08/851,379, herein incorporated byreference) located on the flying head 506 towards a surface recordinglayer 549 of a respective MO disk 507.

During writing of information, the first beam 191 a is selectivelyrouted by the optical switch 104 towards a particular MO disk 507 so asto lower a coercivity of the surface recording layer 549 by heating aselected spot of interest 540 to approximately the Curie point of the MOrecording layer 549. The optical intensity of the first beam 191 a isheld constant at a power in a range of 30-40 mw, while a time varyingvertical bias magnetic field is used to define a pattern of “up” or“down” magnetic domains perpendicular to the MO disk 507. This techniqueis known as magnetic field modulation (MFM). Subsequently, as theselected spot of interest 540 cools at the surface layer 549,information is encoded at the surface of the respective spinning disk507.

During readout of information, the first beam 191 a (at a lower powercompared to writing) is selectively routed to the MO disk 507 such thatat any given spot of interest 540 the Kerr effect causes a reflectedlaser beam 192 (a reflection of the first beam 191 a from the surfacelayer 549) to have a rotated polarization of either clockwise or counterclockwise sense 563 that depends on the magnetic domain polarity at thespot of interest 540. The reflected laser beam 192 is received by theoptical elements on the MO head 506 and is directed by the set ofoptical elements on the flying head 506 for subsequent electronicconversion and readout.

Referring now to FIGS. 6a-6 b, the directing optics are illustrated infurther detail. The directing optics 375 (FIG. 3d) includes: an upperportion 675 a and a lower portion 675 b; both are coupled to a mountingportion 675 c. In the preferred embodiment, the outgoing laser beam 191is directed by the first actuator 333 through the lower portion 675 band is optically separated by the lower portion 675 b into the firstbeam 191 a and a fourth beam 191 d. The lower portion 675 b directs thefirst beam 191 a towards the redirection lens 311 generally along orabout a central optical axis of the redirection lens 311. The lowerportion 675 b also directs the fourth beam 191 d towards the upperportion 675 a. The fourth beam 191 d is optically separated by the upperportion 675 a into the second beam 191 b and the third beam 191 c. Thesecond beam 191 b is directed by the upper portion 675 a towards theredirection lens 311 along an optical axis that is generally parallel tobut not co-extensive with the aforementioned central optical axis of theredirection lens 311. The upper portion 675 a also directs the thirdbeam 191 c towards the first detector 358. Those skilled in the art willrecognize that the upper portion 675 a and lower portion 675 b maycomprise beam-splitters of a variety well known in the optical arts.Those skilled in the art will also recognize that in the presentinvention optical displacement of the outgoing laser beam 191 willresult in analogous displacements of the first, second, and third beams191 a-c. The displacements of the first, second, and third beams 191 a-cwill be utilized to effect an optical switching function as is describedin further detail below.

Referring back to FIGS. 3a-e, in an exemplary embodiment, the firstactuator 333 comprises a flat voice coil motor assembly (VCM), describedin further detail below. In the preferred embodiment, rotation of thearm 371 by the first actuator 333 positions the reflector 373 such thatthe optical path traversed by the outgoing laser beam 191 is deflectedin a plane that is parallel to a linear axis defined by the array oflenses 476. The outgoing laser beam 191 is directed by the reflector 373through the directing optics 375, towards the redirection lens 311 andthe array of lenses 476, and through a particular lens 476 toward aparticular proximal end of the optical fibers 302. In an exemplaryembodiment, the first actuator 333 operates with an open loopcompensated crossover frequency of approximately 0.4 Khz and is capableof approximately 200 g's of acceleration. In the exemplary embodiment,the first actuator 333 rotates the arm 371 about pivot axis P over a+/−3.5 degree range of motion. The following performance characteristicsare exhibited by the optical switch 104 using the first actuator 333:829 um deflection of the first beam 191 a across the front surface of aparticular lens 476 and 55 um deflection of the first beam 191 a acrossa proximal end of the optical fibers 302 per degree of rotation of thearm 371; and 0.1 um alignment accuracy of the first beam 191 a onto aproximal end of the optical fibers 302 per 1.5 um of deflection of thefirst beam 191 a across the array of lenses 476.

Referring now to FIGS. 3e and 7 a-e, the first actuator 333 of thepresent invention is illustrated in further detail. The first actuator333 includes a set of generally planar assemblies comprisingcross-hinges 9 and 22 that are disposed between a set of extended arms41, 42 and a rigid mounting base 300. The set of hinges 9 and 22 of thepresent invention replace the pivot and bearing assembly of prior artmotors. In an exemplary embodiment the hinges are used in conjunctionwith a voice-coil motor (“VCM”).

Referring now to FIGS. 3e and 7 a, there are seen a perspective view ofthe first actuator 333 including: a first hinge 10, a second hinge 11, athird hinge 23, and a fourth hinge 24. In the preferred embodiment, thehinges 10, 11, 23, and 24 are shaped as generally planar rectangles,however, as will be understood below, depending on the performancecharacteristics desired, the hinges 10, 11, 23, and 24 may compriseother shapes, for example, generally planar squares, etc.

Referring now to FIG. 7b, there is seen a view of the first hinge 10 andthe second hinge 11 attached to respective fixed support 30 and movablesupport 31. First hinge 10 includes a first end 13 that is attached to anotched upper portion of the movable support 31 and a second end 12 thatis attached to a notched (notch not visible) upper portion of the fixedsupport 30. Second hinge 11 includes a first end 15 that is attached toa notched lower portion of the movable support 31 and a second end 14that is attached to a notched lower portion of the fixed support 30. Inthe preferred embodiment, attachment of the ends of the hinges 10 and 11to the supports 30 and 31 may be performed utilizing epoxy or a suitableadhesive; it is understood, however, that other methods of attachmentare also within the scope of the present invention, for example, screws,rivets, etc. Hinges 23 and 24 are attached to fixed support 50 andmovable support 51 in a similar manner.

Referring now to FIG. 7c, the first hinge 10 and the second hinge 11 areviewed to comprise an upper pair of cross-hinges 9, which in a top viewcross each other in an “X” shaped manner.

Referring now to FIG. 7d, the third hinge 23 and the fourth hinge 24 aresimilarly attached to fixed supports 50 and 51 and form a lower pair ofcross-hinges 22.

Referring now to both FIG. 3e and FIGS. 7a-d, the movable supports 31and 51, and the fixed supports 30 and 50 each include eight faces A-H,including a top and bottom face G and H, respectively. The faces A-H ofthe movable supports 31 and 51 correspond to the faces A-H of the fixedsupports 50 and 51, respectively. The face A of the fixed support 30 isattached to an upper side of the rigid mounting base 300. The bottomface H of the movable support 31 is attached to a top surface of anupper extended arm 41. The face A of the fixed support 50 is attached toa lower side of the rigid mounting base 300. The upper face G of thefixed support 51 is attached to an area of a bottom surface of a lowerextended arm 42.

Referring back to FIG. 3e and FIG. 7a, the first actuator 333 includes acoil 900 disposed between a first magnet 70 and a first cold-rolledsteel block 60, and a second magnet 80 and second cold rolled steelblock 90. The coil 900 is attached to the actuator arm 371. The actuatorarm 371 connects to two extended arms 41 and 42. The reflector 373 isattached to the coil support 900 between the extended arms 41 and 42.The coil 900 includes an input and an output whereat a current may beapplied by a current source (not shown). In an embodiment where supports30, 31, 50, and 51 are not conductive, the input and output may attachto different ones of the hinges 10, 11, 23, 24. In other embodiments,the input and output may attach to different ones of the supports 30 and50, or 31 and 51. The input and output may also be attached otherpoints, for example, to a point somewhere in space.

Referring now to FIG. 7e, there is seen a representative top view of amovement of the hinges 10 and 11. In the preferred embodiment,application of a current to the input of the coil 900 creates a magneticfield opposite to the magnetic field of the magnets 70, 80. The opposingmagnetic fields create a repulsion force that moves the arm 371 awayfrom the magnets 70, 80 (shown as an exemplary direction A). Asdiscussed below, because the arm 371 is coupled through the extended arm41 to the movable support 31, when current is applied to the coil 900,the movable support 31 will also move (shown as an exemplary directionW).

With reference to cross hinges 9, because the first ends 13 and 15 ofthe hinges 10 and 11 are rigidly attached to the fixed support 30 alongrespective surfaces C and E, any independent movement of the second ends12 and 14 of the hinges 10 and 11 may occur along an extent of thesecond ends and with an angle theta. Those skilled in the art willrecognize that in an embodiment in which the hinges 10 and 11 compriserigid material, attachment of the second ends 12 and 14 to the movablesupport 31 would fixidly constrain the movable support 31 in free space.In the present invention, however, the hinges 10 and 11 comprise asufficiently flexible material such that application of a force to themovable support 31 will result in a constrained rotation of the secondends 12 and 14 and, thus, the movable support 31 about a pivot axispassing generally through a region P. The pivot axis is generallydefined by a flexure point of the hinges 10 and 11 and corresponds tothe center of the “X” shape described in FIG. 7c. In an exemplaryembodiment, the hinges 10, 11, 23, and 24 are rigid enough such that thearm 371 rotates without excessive up, down, or torsional motion and yetare flexible enough that the arm 371 rotates without excessivedisturbances through its +/−3.5 degree range of angular motion. In thepreferred embodiment, the hinges 10, 11, 23, and 24 comprise a singlelayer 0.0015 inch thick stainless steel material. In an alternativeembodiment, the hinges 10, 11, 23, and 24 may comprise a 0.001 inchlayer stainless steel layer, a 0.001 inch viscoelastic layer, and a0.001 inch plastic layer. Also, the hinges 10, 11, 23, and 24 preferablydo not exhibit undesirable resonance over the desired operatingbandwidth of the first actuator 333. The aforementioned discussion ofFIG. 3 is understood to also apply to hinges 23 and 24.

When current is applied to coil 900, the combination of uppercross-hinges 9 and lower cross-hinges 22 act to center the rotationalmovement of the arm 371 (i.e., direction A) and thus the movable support31 (i.e., direction W) parallel to a plane passing between the magnets70 and 80. In the present invention, although the movable support 31rotates about the pivot axis within the region P with the angle theta,the flexure of the hinges 10 and 11 causes a translation of the pivotaxis (i.e., in a direction T). Thus, the region P through which thepivot axis passes is defined by the flexure point of the cross hinges 9and 22 as well as the extent of translational motion T.

Those skilled in the art will recognize that the cross-hinges 9 and 22of the first actuator 333 are advantageous over prior art bearings as nofrictional forces exist between bearing surfaces. In the presentinvention, the hinges 10, 11, 23, and 24 exhibit hysteresis effects.However, in the present invention, the hysteresis effects are preferablysmaller than the frictional forces of the prior art. The reducedfrictional forces of the present invention result in a reduced currentas compared to the prior art current required to impart movement with agiven force to the arm 371. Furthermore, for a required given force, thecoil 900 may be made smaller than the prior art. A smaller coil reducesthe mass such that rotation may occur about the pivot axis with anincreased speed and improved operating bandwidth. Also, in the presentinvention, the cross hinges 9 and 22 are not limited by a minimum sizeas are commercially available bearings, and, therefore, the firstactuator 333 of the present invention may be made with a smaller formfactor than the prior art. While implementation of a set of hinges 10,11, 23, and 24 has been described in a voice coil motor embodiment, itis understood that the hinges 10, 11, 23, and 24 could also be used inother types of actuators to effect other types of displacements, forexample mechanical displacements and the like and, therefore, the hinges10, 11, 23, and 24 of the present invention should be limited only bythe scope of the following claims.

Referring back to FIGS. 3a-e, in the preferred embodiment, the firstdetector 358 is disposed in the optical path traversed by the third beam191 c (in direction 356) such that positional output signal provided bythe first detector 358 corresponds to positional displacement of theoutgoing laser beam 191 by the arm 371. The first detector 358 comprisesa position sensing detector (PSD) of a variety well known in the art. Inan exemplary embodiment, the first detector 358 comprises aone-dimensional 1×7 mm PSD manufactured by Hamamatsu Photonics K.K,Hamamatsu City, Japan that exhibits operating characteristics that aresimilar to Hamamatsu PSD model no. S3931. As described in an exemplarymethod of use in further detail below, displacement of the first beam191 a across the array of lenses 476 also corresponds to positionaldisplacement of the outgoing laser beam 191 by the arm 371. Positionaloutput signals provided by the first detector 358 can, thus, be used toascertain the position of first beam 191 a with respect to a particularlens 476. In the preferred embodiment, the positional output signalsprovided by the first detector 358 are used with a feedback servocircuit (e.g., illustrated in FIG. 9 as an AD880 manufactured by AnalogDevices, Norwood, Mass.) to provide an input signal to the coil 900 ofthe first actuator 333 and, thus, to controllably direct the first beam191 a (in one-dimension) towards a desired optical fiber 302.

Referring back to FIGS. 3a-e again, in the preferred embodiment, thesecond actuator 334 comprises a two stage voice-coil motor (VCM) of avariety well known in the art. In an exemplary embodiment, theredirection lens 311 is coupled to the second actuator 334 using wellknown optical mounting techniques such that 0-350 um of motion can beimparted by the second actuator 334 to the redirection lens 311 in oneor both of the indicated directions 356, 379.

In the preferred embodiment, the redirection lens 311 receives the firstbeam 191 a, and the second actuator 334 controllably directs the firstbeam 191 a (in two dimensions) towards a particular lens 476 and, thus,towards a desired optical fiber 302. In the preferred embodiment, theredirection lens 311 also receives the second beam 191 b and directs thesecond beam 191 b towards the second detector 359. As described in anexemplary method of use in further detail below, displacement of thefirst beam 191 a across the array of lenses 476 also corresponds topositional displacement of the second beam 191 b by the second actuator334. Positional output signals provided by the second detector 359 can,thus, also be used to ascertain the position of first beam 191 a withrespect to a particular lens 476. In the preferred embodiment, thepositional output signals provided by the second detector 359 are usedwith a feedback servo circuit (e.g., illustrated in FIG. 11 as an AD880manufactured by Analog Devices, Norwood, Mass.) to provide an inputsignal to the second actuator 334 and, thus, to controllably direct thefirst beam 191 a (in two-dimension) towards a desired optical fiber 302.

In the exemplary embodiment, the second actuator 334 operates with anopen loop compensated crossover frequency of approximately 1.5 Khz andis capable of 100 g's of acceleration. In the aforementioned embodiment,the resulting performance characteristics are desired: 59 um ofdisplacement of the first beam 191 a across a particular lens 476, 56 umof displacement of the first beam 191 a across a proximal end of theoptical fibers 302, and 150 um displacement of the second beam 191 bacross the second detector 359, per 1000 um of linear displacement ofthe redirection lens 311 by the second actuator 334. One benefit derivedfrom use of the redirection lens 311 with the second actuator 334 in theoptical path of the outgoing beam 191 is that reduced mechanicaltolerances are possible for achieving alignment of the outgoing laserbeam 191 onto a particular lens 476.

Referring now to FIG. 8, there is seen an exemplary geometry of thesecond detector. In the preferred embodiment, the second detector 359comprises a quad photo-detector array. As illustrated in dimensionaldetail in FIG. 8, the second detector 359 comprises a plurality ofphoto-detector pairs that are alternatively and adjacently disposedalong a generally semicircular arc. Those skilled in the art willrecognize that the measurement surfaces of adjacent photo-detector pairscan be used with well known quad array detection techniques to detectand measure the position of the second beam 191 b across the measurementsurfaces.

FIG. 10 illustrates outputs of A-D photo-detectors and their connectionsto the servo circuit illustrated in FIG. 11. The servo circuit utilizesA-D photodetector outputs to provide the second actuator 334 withvertical and horizontal error signals for positioning of the redirectionlens 311. In the preferred embodiment, the semicircular arc along whichthe A-D photo-detectors are disposed is a function of the location wherethe second beam 191 b is deflected through the redirection lens 311 bythe first and second actuators 333, 334. Those skilled in the art willrecognize that the shape of the semicircular arc depends on variousparameters, including: the size of the redirection lens 311, thedistance between the lenses 476, the distance between the redirectionlens 311 and the second detector 359, and the desired performancecharacteristics. In an exemplary embodiment, the second detector 359 isdisposed in the optical path of the first beam 191 a such that 100 umdisplacement of the second beam 191 b across the second detector 359corresponds to 33 um of displacement of the first beam 191 a across aparticular proximal end of the optical fibers 302.

Those skilled in the art will recognize that at higher operatingfrequencies (i.e., higher switching speeds of the optical switch 104)the servo circuitry and, thus, the first and second detectors 358, 359will exhibit a concomitant increase in output noise, which will act todecrease the positional accuracy with which the first beam 191 a may bedirected towards the optical fibers 302. It is also understood thatother sources of high frequency noise may also be present, for example,noise resulting from shock, vibration, optical, and/or thermal effects.The positional accuracy with which the first beam 191 a may be directedis a function of the positional output signal SNR provided by the firstand second detectors 358, 359. Because the output signals provided bythe first detector 358 are obtained across a wider measurement surfacethan from the second detector 359 and because a 0.5 um positionalaccuracy of the first beam 191 a onto a particular lens 476 is desiredfrom both the first and second actuators 333, 334, a given amount ofoutput noise will comprise a larger percentage of the positional outputsignal provided by the first detector 358 than the second detector 359.In the preferred embodiment, the SNR of positional output signal fromthe first detector 358 may be increased by passing the signal through alowpass filter to effectively reduce the high frequency noise componentsresulting from, for example: the servo circuit itself, shock, vibration,optical, and/or thermal effects. However, those skilled in the art willrecognize that reduction in high frequency noise may result in adecrease in the operating bandwidth over which the first actuator 333can be used to deflect the outgoing laser beam 191.

The present invention overcomes this limitation by using the relativelylow-bandwidth first actuator 333 for coarse optical positioning thefirst beam 191 a over a wide surface area (i.e., the entire array oflenses 476) in conjunction with the relatively hi-bandwidth secondactuator 334 for fine optical positioning of the first beam 191 a over arelatively narrow surface area (i.e., a particular lens 476). The use ofa hi/low bandwidth actuator combination preferably eliminates the needfor very expensive low/noise/high-frequency servo electronics that wouldbe required when using a single actuator for fast and precise opticalswitching of light between the input port 181 and the output ports 182.

In an exemplary embodiment, switching the first beam 191 a between theoptical fibers is made up of a two stage process: 1) positioning thefirst beam 191 a between lenses 476 using the first actuator 333 with asettling accuracy of about 1 um and within about 3 ms; and 2) finepositioning the first beam 191 a to a new position over a particularoptical fiber 302 within about 1 ms. In the aforementioned process, theopen loop acceleration portion of the second actuator 334 preferablyoverlaps the motion of the first actuator 333 to reduce the amount ofmotion required by the second actuator 334.

Referring now to FIG. 12, an exemplary embodiment ofpre/post-calibration of the optical switch 104 is illustrated and isdescribed as follows. Initially, the first actuator 333 (FIGS. 3a-3 e)positions the reflector 373 towards one extreme of the rotationindicated as 355 to reflect the outgoing laser beam 191, and the secondactuator 334 (FIGS. 3a-3 e) positions the redirection lens 311 towardsone extreme in the direction indicated as 356 and towards a secondextreme in the direction indicated as 359. The first beam 191 a is thusdirected towards the array of lenses 476, however, the first beam 191 ais at this point not necessarily optimally focused by a particular lens476 towards a particular optical fiber 302. Next, the reflector 373 isscanned in the direction 355 until a first increase in the amplitude ofthe reflected laser beam 192 (FIG. 5) is detected. If after rotation inthe direction 355 an increase in the amplitude of the reflected laserbeam 192 is not detected, the reflector 373 is again positioned towardsone extreme of the rotation 355 and the second actuator 334 isincremented in the vertical direction 356 and the reflector 373 is thenagain scanned in the direction 355. The aforementioned process isrepeated until a first increase in amplitude in the reflected laser beam192 is detected (Point A). At point A, the second actuator 334 isalternatively incremented horizontally and vertically in the directions356 and 379 until a maximum amplitude of the reflected laser beam 192 isobtained. A maximal value preferably corresponds to optimal alignment ofthe first beam 191 a over the optical axis of a first of the array oflenses 476. As previously described above, point A will thus correspondto values measured by the first and second detectors 358, 359 (FIG. 3e).These values are stored for subsequent positioning of the first beam 191a towards the first lens of the array of lenses 476 (only two lensesshown). The position over the lens is maintained utilizing the first andsecond actuators 333, 334 and their respective servocircuits. Thoseskilled in the art will recognize that, as previously described, theposition of any remaining lenses 476 can also be determined throughappropriate scanning in the directions 355, 356, and 379 whilemonitoring the reflected laser beam 192 for respective increases inamplitudes. The output values measured by the first and second detectors358 and 359 at the respective maximum amplitudes of the reflected laserbeam 192 can, thus, be used to preferably position the first beam 191 atowards any one of the array of lenses 476 and, thus, towards any one ofthe optical fibers 302. The calibration sequence described above can beutilized to adjust for subsequent misalignments resulting from, forexample, shocks and temperature. Those skilled in the art will alsorecognize that the method of use described above should not limit thepresent invention, as other methods of use are also within the scope ofthe invention, which should be limited only by the scope of the ensuingclaims.

Referring now to FIG. 13a, an embodiment of a magneto-optical disk driveis illustrated. In an exemplary embodiment, the magneto-optical (MO)data storage and retrieval system 500 comprises an industry standard5.25 inch half-height form factor (1.625 inch) within which are disposedat least six double-sided MO disks 507 and at least twelve flying MOheads 506. The flying MO heads 506 are manufactured to include 12optical fibers 302 as part of a very small mass and low profile high NAoptical system so as to enable utilization of multiple MO disks 507 at avery close spacing within the system 500 and; therefore, to comprise ahigher areal and volumetric and storage capacity than is permitted in anequivalent volume of the prior art. In the preferred embodiment, aspacing between each of the at least six MO disks 507 is reduced to atleast 0.182 inches. High speed optical switching between the lasersource 131 and the MO disks 507 is provided by the optical switch 104and the first actuator 333 contained therein.

In the present invention, when the outgoing laser beam 191 is alignedover a particular lens 476, the output port 182 from which the outgoinglaser beam 191 exits towards a particular MO disk 107 may be identifiedby a sensing a signal from outputs of the corresponding A-Dphoto-detectors of the second detector 359, for example, a maximum in asummed signal of the outputs of a particular set of A-D photo-detectors.The signals from the sensing circuit may be used subsequently toidentify which of the set of MO disks 107 is being read or written atany given time. This compares to the prior art that requires MO disks beidentified by data marks written to the MO disks.

In an alternative embodiment shown in FIG. 13b, the system 500 mayinclude a removable MO disk cartridge portion 710 and two fixed internalMO disks 507. By providing the removable MO disk cartridge portion 710,the fixed internal and removable combination permits externalinformation to be efficiently delivered to the system 500 for subsequenttransfer to the internal MO disks 507. The copied information may,subsequently, be recorded back onto the removable MO disk cartridgeportion 710 for distribution to other computer systems. In addition, theremovable MO disk cartridge portion 710 allows for very convenient andhigh speed back-up storage of the internal MO spinning disks 507. Thefixed internal and removable combination also permits storage of datafiles on the removable MO disk cartridge portion 710 and system filesand software applications on the internal MO spinning disks 507. Inanother alternative embodiment (not shown) system 500 may include: anynumber (including zero) of internal MO disks 507 and/or any number of MOdisks 507 within any number of removable MO disk cartridge portions 710.

While the present invention is described as being used in an MO diskdrive system 500, the optical switch 104 and the first actuator 333contained therein may be used in many different environments and manydifferent embodiments, for example, with first and second actuatorsother than voice-coil motor actuators, with other form factors, withother optical sources of light, with other types of optical fibers,and/or with other types of optical elements. The optical switch 104 isalso applicable to information transfer using other head technologies,for example, optical heads in compact disks (CD) and digital video disks(DVD). The optical switch 104 of the present invention can also be usedfor optical switching of light in other optical communicationsapplications, e.g., fiber optic communications.

Thus, the present invention has been described herein with reference toparticular embodiments thereof, a latitude of modification, variouschanges and substitutions are intended in the foregoing disclosure andit will be appreciated that in some instances some features of theinvention will be employed without a corresponding use of other featureswithout departure from the scope of the invention as set forth.

What is claimed:
 1. A method of deflecting a beam of light between aninput and an output of an optical switch comprising the steps ofcoarsely directing said beam of light in response to low frequencycontrol signals and finely directing said beam of light in response tohigh frequency control signals.
 2. The method of deflecting a beam oflight as recited in claim 1 wherein said coarsely directing step occursprior to said finely directing step.
 3. An optical switch for deflectinga beam of light between an input and an output of the optical switch inresponse to low frequency and high frequency control signals, comprisinga first beam deflector disposed in an optical path of said beam of lightbetween said input and said output for coarsely directing the beam oflight in response to the low frequency control signals and a second beamdeflector disposed in said optical path of said beam of light betweensaid input and said output for finely directing the beam of light inresponse to the high frequency control signals.
 4. The optical switch asrecited in claim 1, wherein said first beam deflector comprises a voicecoil motor.
 5. The optical switch as recited in claim 4, wherein saidfirst beam deflector directs said beam of light towards said second beamdeflector in one dimension.
 6. The optical switch as recited in claim 4,wherein said first beam deflector comprises a rotary arm and a reflectorcoupled to said arm for directing said beam of light.
 7. The opticalswitch as recited in claim 1, further comprising a position sensingdetector for sensing a position of a portion of said beam of light andcontrolling the direction of said beam of light by said first beamdeflector as a function of said sensed position of said portion of saidbeam of light.
 8. The optical switch as recited in claim 1, wherein saidsecond beam deflector comprises a two-stage voice coil motor.
 9. Theoptical switch as recited in claim 1, wherein said second beam deflectordirects said beam of light in two dimensions.
 10. The optical switch asrecited in claim 1, wherein said second beam deflector comprises adirecting lens for directing said beam of light.
 11. The optical switchas recited in claim 10, further comprising a quad detector array forsensing a position of a portion of said beam of light and controllingthe direction of said beam of light by said second beam deflector as afunction of said sensed position of said portion of said beam of light.12. The optical switch as recited in claim 1, further comprising anarray of lenses in the vicinity of said output, said first and saidsecond beam deflectors selectively directing said beam of light towardssaid array of lenses.
 13. The optical switch as recited in claim 12,wherein said array of lenses comprises a linear array of adjacentlenses.
 14. An optical storage drive, comprising a disk having anoptical storage location and an optical switch for deflecting a beam oflight between an input and an output of the optical switch, said opticalswitch having a first beam deflector disposed in an optical path of saidbean of light between said input and said output for coarsely directingthe beam of light in response to low frequency control signals and asecond beam deflector disposed in said optical path of said beam oflight between said input and said output for finely directing the beamof light in response to high frequency control signals.
 15. The storagedrive as recited in claim 14, wherein said output comprises opticalfibers for directing said beam of light towards said optical storagelocation.
 16. The storage drive as recited in claim 14, wherein saidsecond beam deflector is disposed in said optical path between saidfirst beam deflector and said output.
 17. The storage drive as recitedin claim 16, wherein said first and second beam deflectors each includea voice-coil motor.
 18. An optical switch for deflecting a beam of lightextending along an optical path in response to low frequency and highfrequency control signals, comprising a first deflector disposed in theoptical path for coarsely directing the beam of light in response to thelow frequency control signals and a second deflector disposed in theoptical path of the coarsely directed beam of light for finely directingthe beam of light in response to the high frequency control signals. 19.The optical switch as recited in claim 18, wherein the first deflectorincludes a first actuator and a reflector coupled to the first actuatorfor directing the beam of light.
 20. The optical switch as recited inclaim 19, wherein the first actuator is a rotary actuator.
 21. Theoptical switch as recited in claim 19, wherein the second deflectorincludes a second actuator and a lens coupled to the second actuator fordirecting the beam of light.